It depends on the species of Bluey. What species have you been looking at? Tanimbars only get like 15 inches but they are feisty and Meraukes can be as long as 30 inches.
The average Bluey on the market ( Northen and Ij) are 16 to 24 inches.

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1.0 Indonesian Blue Tongue Skink (Don)
0.1 Irian Jaya Blue Tongue Skink (Sausage Girl)
0.0.1 Tanimbar Island Blue Tongue Skink ( Spunky Sebastian)
1.0.1 Green Tree Pythons ( Male=Floyd, Baby= Verdi)
0.1 Western Hognose (Piggy)
0.0.1 Egyptian Tortiose(Tank)
0.0.1 Sonoran Gopher snake ( Toro)
0.1 Albino Leo gecko (Sasha)
1.1 African Greys (Timmy and sis)
1.0 White bellied Caique (Diego)
0.1 Goffin's Cockatoo ( Sydney)
3.1 Ferrets (Chase, Angel, Max, and King)
1.0 Greater Swiss Mountain Dog (Moose)